Variable Frequency Drives (VFD) Power Loss Ride Through

OTP Industrial Solutions for Electrical Applications
Written by Tim Griffith
October 22, 2009

lightningVariable Frequency Drives (VFD) are commonly used in industrial applications. However, the sensitive components of VFD’s are often susceptible to Power Loss, Power Dips and Brown-Out conditions, which may cause the VFD and the entire system to shut down.

Fortunately there are several solutions for power interruptions. Some VFD manufacturers have incorporated specific algorithms in the software and, with just a few programming changes, the VFD can withstand most of these conditions.

Recently a customer contacted me about a power loss condition which was causing his VFD to drop out.  His VFD (which controls his air compressor) had to be restarted each time by issuing a start command separate from the machine it was controlling.  The customer asked me if there was anything that I could do to allow his drive to stay powered up during a Power Loss lasting up to three seconds.

Depending on the manufacturer and model of the VFD – and its programming – the drive can store the energy from its capacitor banks for a predetermined amount of time before dropping out and losing power.  Think of it this way; if you turn off a VFD, the lights remain on for a few seconds before it is totally powered down.  The software can utilize this stored energy to maintain the VFD through a short intermittent Power Loss.

Furthermore, the good news for my customer was that even if it is a long Power Loss, I showed him how to program a second set of parameters in a VFD to restart automatically.  Note: starting automatically needs to be analyzed for safety first before programming that function)

I helped my customer reprogram his drive, and his VFD (and his air compressor) is now able to “ride-through” intermittent power losses.

Moral of this story: There are many features available in most VFDs…and I can help you take advantage of these features.

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